Data transmissions using the Internet are becoming increasingly useful in conducting business-to-business (B2B) and business-to-consumer/customer (B2C) transactions. Payment systems and messaging systems are widely used to transfer data across the Internet. Often, the senders of such data desire to receive confirmation of receipt of data returned from the intended recipients. For example, conventional email systems can support a return receipt feature. In a conventional email system, a return receipt indicates that “a user” has received the intended message. However, the return receipt does not guarantee that the intended recipient has received the intended message, because anyone, including the sender, can easily forge such a receipt. In addition, there are usually many ways for the recipient to read the message without sending the receipt. What is desired is a system that allows the sender to obtain an irrefutable proof that the recipient has received a particular message/data. In addition, the system should prevent the sender from obtaining such proof unless the message/data has actually been delivered to the recipient. In many situations, it may also be desirable to have an irrefutable proof that the message/data was sent and received at specific times.